For the past nine years, the Transplantation Biology Unit at UCLA has been involved in a continuing program of bone marrow transplantation in the treatment of patients with aplastic anemia, leukemia, cancer, and immunodeficiency diseases. Many of these patients have become long-term survivors but considerable problems remain to be addressed including prevention of graft rejection, graft-vs-host disease (GVHD), delay of immune reconstitution and interstitial pneumonia. This proposal outlines our ongoing studies in three major program areas: (1) the immunobiology of marrow transplantation, and (3) interstitial pneumoia in transplant recipients. These studies include preclinical studies in dogs, and controlled clinical trials. The objective of the proposed project is to continue progress in the application of bone marrow transplantation to human disease by an in-depth analysis of basic problems of transplantation biology in animals and by appropriate clinical trials.